This invention relates generally to an apparatus for treating the semiconductor wafer so that individual units which may be single devices or complex integrated circuits can be easily separated from the semiconductor wafer in which they are formed. More particularly, the invention relates to an apparatus that aligns a semiconductor wafer to a fixed reference and emits an aligned laser beam to traverse the reverse side of the wafer such that easily fractured regions can be created in the region of the wafer traversed by the laser beam.
Methods and apparatus for dividing semiconductor devices from monolithic wafers and sorting the semiconductor devices are known. One such apparatus shown in U.S. Pat. No. 3,583,561 tests each device in a wafer optically, encodes the test data, and prepares a photographic record thereof. After testing the wafer is mounted on a pressure sensitive web together with the coded photographic record and the wafer broken to separate the respective devices. By reading the coded record, output signals can be utilized to pick each of the separated devices from the web and placed into a preselected station with devices of common characteristics. Unless great care is taken in mounting the photographic record and the wafer significant discrepancies in the removal of the selected devices will occur.
It is also known that substrates can be aligned prior to laser dicing as is taught in U.S. Pat. No. 3,816,700. This patent discloses the alignment of a wafer with its active face up, in a portable vacuum chuck that will hold the aligned wafer in a set position. Once the wafer is aligned the portable vacuum chuck is then transferred to a holding device which can be placed under a laser scribing apparatus which scribes the active face of the aligned wafer with a laser beam in accordance with the preset alignment. The action of the laser beam in dicing the wafer creates a residue on the face of the wafer which can interfere with the subsequent handling and mounting of the diced units.
To avoid this, the concept of laser dicing from the backside of the wafer away from the active units was considered. Such cutting of semiconductor wafers from the reverse side with the laser beam is taught in U.S. Pat. No. 3,824,678 which teaches that a wafer can be aligned in an inverted position by using an infrared microscope and subsequently dicing the wafer. Such infrared microscopes have poor resolution thus requiring that the units to be separated from the wafer be created further apart in the wafer so that the poor infrared resolution can be compensated for. Additionally such infrared microscopes are complex, difficult to use, and expensive to purchase. Also they do not permit direct viewing of the semiconductor wafer surface.
Accordingly, the present invention which describes a complete system for the dicing of individual semiconductor units from an integral wafer avoids the difficulties and disadvantages encountered by these prior art systems.